Research is directed toward the elucidation of the mechanism whereby sensitized T cells are triggered by antigen-bearing macrophages. The specificity requirements that must be satisfied for stimulation of Listeria-immune T cells are being analyzed in inbred strains of rats. The consequences of T cell triggering also are being defined from the standpoint of mediator production and the ability of these mediators to promote the deployment of T cells and macrophages at sites of bacterial implantation. The above stimlus make use of cell transfer methods, "purified" populations of T cells, radiolabeling techniques and a variety of inbred strains of rats that differ with respect to their MHC genotype.